1. Field of the Invention
This invention relates to an apparatus for washing tanks to clean out, for example, sludge and other such solid matter that collects at the bottom of crude oil tanks and other such tanks used to store relatively large quantities of liquid, and to a tank washing method using the apparatus.
2. Description of the Prior Art
Manually washing out large-capacity tanks such as tanks used to store crude oil is a lengthy process, involving as it does the risk of fire and health risks in a closed environment. In addition, it is difficult to recover oil components from tank sludge. Owing to such factors, a method of washing tanks that is in widespread use involves the use of a machine that emits a pressurized jet spray of washing liquid, the machine being installed in the floating roof or other such roof portion of the tank with the spray directed into the tank. Sludge that has collected at the bottom of the tank is thus broken down and cleaned out by spraying the sludge with clean oil or the like under pressure (U.S. Pat. No. 4,426,233).
At the time of the washing process the floating roof in which the spraying machine is installed is at a height of around two meters from the floor of the tank. This means that the effective floor washing distance of the washing liquid sprayed from the spraying machine is short, which necessitates the installation of multiple spraying machines. A floating roof type tank having a diameter of 100 meters and a height of 20 meters, for example, is equipped with some 35 spraying machines. However, this type of arrangement has a number of problems, including the following.
1. Many spraying machines are required. Large quantities of equipment such as pipes and valves, are required for the temporary installations.
2. Installing and removing the equipment requires a lot of man hours and time.
3. Large lifting equipment is required to hoist the equipment onto the roof and remove it.
4. The large number of spraying machines involved makes the operation and maintenance thereof complicated.
5. While an installation may comprise as many as 30 or more spraying machines, there are times when only two or three can be operated, so the operating efficiency of the spraying machines is poor.
6. Replacement and maintenance of spraying machines take time and work, with the workers involved having to raise and lower the tank of 20-meter height each time. Thus, any problems such as leaks happening to equipment on the roof cannot be promptly tackled.
7. Some roof supports are removed to install spraying machines, increasing the load on the surrounding parts of the removed roof supports, which is undesirable in terms of strength and safety.
8. The large numbers of man hours and large quantities of equipment involved push up the costs.
An object of the present invention is to provide a tank washing apparatus and method that can be readily set up, reliably fluidize accumulated solid matter such as sludge and efficiently expel the same from the tank, regardless of what liquid has been stored in the tank.